Custom printed plastic cards find use in a wide variety of applications such as patient ID, sports tickets, hotel keys, company or school ID, and the like. Such cards should provide high quality images as well as being easy to produce, flexible, durable, and low cost. In the case of identity cards there may be significantly greater requirements to prevent forgery or unauthorized use. These printed plastic cards should be tamper proof and provide additional levels of security such as UV or IR readable information, magnetic strips, 2D bar codes or RFID chips.
A number of techniques can be utilized to produce printed plastic cards or sheets.
For example, toner-based printers can easily print images on many types of plastics such as PVC, polyester, polycarbonate or polyketone, depending on the fusing temperature of a particular printer. However, typical toner-based images can easily be damaged by abrasion and can also be altered to produce a forged document. Likewise, inkjet or traditional offset printing techniques can provide acceptable printed images although these are also not durable or tamper-proof unless laminated which in itself provides a more complex solution. Thermal transfer printing is another technique that can be used to provide printed plastic images. In this case a polymer or wax layer is image-wise transferred from a release backing to the plastic. Such images are also not tamper-proof or abrasion resistant unless laminated or over-coated with a protective layer. In each of the above techniques a second overcoat or lamination step is required to achieve a level of permanence and tamper-resistance.
Another printing process for decorating plastic sheets is referred to as “dye-sublimation” where pre-coated dye layers on a backing layer are placed in contact with the receiver sheet and individual thermal heads used to image-wise transfer the dye only to the plastic. Actually, this process is not true dye sublimation which would mean the dyes transfer from a solid state to a gaseous state, without going through a liquid state. This dye ribbon process is more accurately referred to as dye diffusion as the molten dye diffuses into the substrate. Certain types of plastics such as polyester are receptive to these dyes. Other plastics such as polycarbonate require a separate dye receiver coating. Where the plastic sheet is receptive, the dye migrates into the sheet itself and provides both a level of abrasion and tamper resistance. If it is desired to add an additional security feature such as invisible UV readable information or a magnetic stripe, a separate coating on the dye-based ribbon would be required and that whole layer would transfer as with thermal ribbons. While this process offers an advantage in being a single step, there can be a significant cost for the coated ribbon as much of the dye in many of the color panels is typically not used.
While the current processes used for producing plastic ID cards may be suitable for many purposes, they also suffer from a number of disadvantages. The traditional PVC or polyester cards are not sufficiently durable enough or tamper-proof for many applications. The use of pre-coated dye ribbons also creates a significant amount of wasted dye in the portions of the ribbon not used. Also, certain dyes used in dye diffusion printers may not have adequate heat and light stability, particularly for outdoor exposure.
What is desired is a polymer sheet or film that overcomes difficulties with PVC, polycarbonate or polyester sheets.
Polyketone polymers are well known. U.S. Pat. No. 2,495,286 to Brubaker discloses polymers of carbon monoxide and ethylenic unsaturated monomers. U.S. Pat. No. 3,689,460 to Nozaki discloses a process of producing high molecular weight polyketone polymers using palladium catalysts. Extruded sheets of polycarbonate film are also well known as are co-extruded laminates of polycarbonate with a polymer such as polypropylene as disclosed by Ofstein in U.S. Pat. No. 5,064,724. Byrd in U.S. Pat. No. 5,300,338 also discloses coextruded laminates of polyketone with nylon, phenoxy or polyvinylidene polymers. Use of polycarbonate polymers in sublimation transfer sheets have also been disclosed as in U.S. Pat. Nos. 4,021,591 and 4,058,644 to DeVries. In this case the polyketone is of low molecular weight and is designed to be part of a coating solution that would be transferred to a substrate. Polyketone polymers have also been frequently referenced as a component of jet inks. Use of polyketone films have also been disclosed as a component of laminated security documents as in U.S. Pat. No. 8,304,061 where Feldman proposes using a polyketone sheet as part of a laminate core layer for laser imaging. It is also known that polyketone polymers can be infused with disperse dyes as shown in U.S. Pat. No. 5,597,389 to Brown. However, in no case are polyketone films or sheets used as a receptor layer that would be infused with solvent or sublimation dye by either conventional or digital printing processes.